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Unsignalized Median Openings in Close Proximity to Signalized Intersections

Closely spaced full median openings result in a complex pattern of overlapping conflicts. Provision of full access intersections is often provided yet unjustified--leading to high crash rates and reduced mainline capacity--each resulting in poor traffic operations. Restricting access in most cases is the best solution; however, there is little guidance on what parameters for full versus restricted access should be considered. There are obvious safety and operational benefits to restricting access. For instance, closing a full median opening and making an intersection right-in/right-out eliminates all left-turn and crossing maneuvers. This reduces the number of conflict points from thirty-two to four. Converting a full median opening to a directional opening for left turns from the major roadway eliminates left turns from the intersecting connection onto the major roadway and crossing maneuvers. Conflict points are reduced from thirty-two to eight (ten if u-turns from both directions are permitted) in this scenario. In some cases an unsignalized median opening may improve operations of a signalized intersection, but only if designed correctly. Based on current research, the operational and safety problems resulting from unsignalized full median openings--as compared to unsignalized directional median openings--need further investigation. For example, Florida Department of Transportation has a policy of closing or converting unsignalized full median openings to directional openings whenever possible (left turn from the main roadway only). Other examples also exist that need to be analyzed. The objective of the research will be to develop guidelines for closing an existing median opening or converting an existing full median opening to a directional opening. The proposed research should answer the following questions: (1) Using a before-after crash analysis, what are the differences in crash rates at unsignalized full median openings compared to the crash rates at unsignalized directional median openings; (2) Using supplemental conflict analysis methods, what are the frequency and severity of conflicts at unsignalized full median openings compared to unsignalized directional openings as a function of speed, traffic volume, or other attributes; and (3) What is the effect of full median and directional median openings on capacity as a function of the movements at a median opening and volume of these movements, the number of traffic lanes, roadway volume, and the speed at which the vehicle(s) on the roadway was traveling when the conflict occurred, etc. The above data collection and analysis will include the distance from signalized intersection to the unsignalized median opening and the design of the left-turn bay where one is present. Many state and local agencies are reconstructing undivided roadways with a nontraversable median or replacing a continuous two-way left-turn lane with a nontraversable median. These reconstruction actions frequently result in opposition by owners of abutting businesses and request for unsignalized median openings. Rationale based on safety, traffic operations, and effect on business as to when and where an unsignalized median opening may be advantageous (as well as where one should be avoided) will assist state departments of transportation (DOTs) and local governments in gaining acceptance of limiting unsignalized median openings near a signalized intersection. Guidelines for evaluating the safety and operational effects of the proposed location and design of an unsignalized median opening will assist in implementation by state and local agencies.